External hard drive is overheating

I've got this old Seagate Expansion Desktop 3.0 that's hitting temperatures up to 57°C while it's running... Is that actually okay, considering it's the middle of summer?

More or less, you hit the nail on the head—it's probably just the heat. Just double-check if there's a built-in fan that might be choked up with dust. If there isn't one, don't sweat it; the thing was designed to handle it without one...